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Desktop Video AGOCG Report

Aspects of the networks

Until recently, networked multimedia applications have been based mainly on dedicated videoconferencing rooms and video coders/decoders working via high-speed leased circuits or ISDN. However, the movement of multimedia to the desktop means that the applications are beginning to move into networks which were originally designed for more conventional data. This leads to the question of whether it will be packet, cell or circuit switched networks which will be used for the spread of multimedia.

At the heart of this revolution is the dramatic improvement in the price and performance of PCs and technical workstations, with UNIX workstations leading the way. Terminals from companies such as Silicon Graphics Inc., Sun Microsystems Inc. and Digital Equipment Corp. are ubiquitously installed in research and development and engineering environments and these workstations already have sufficient processing power to handle multimedia.

In addition the Windows/Intel based PCs that are widely used in office applications are rapidly catching up. Today's PCs are approximately six times as powerful as they were three years ago. In 1994 this power is set to increase further with the development of Intel's Pentium microprocessor, Apple's PowerPC and IBM's RISC (reduced instruction set computing) offerings. It is likely, therefore, that the multimedia market will now be catered for by dedicated multimedia terminals such as the Indigo workstation, IBM's Ultimedia range and the Macintosh AV range (and their RISC descendents).

Most data terminals are already connected to local area networks (LANs), so it is possible that LANs will be the basis for transmission of multimedia around a single site. These will probably use ATM and a dedicated Ethernet to the desktop.

This means that if the users have LANs, there will not be a need for ISDN which has really been derived from voice communications. The only argument in the favour of ISDN is the unreliability of packet switching of the audio and video bit stream in real time communication, but this concern has been refuted by recent developments in the area.

Most of the early use of multimedia has been on the Internet, due primarily to the availability of public domain software tools that allow video and audio to be coded and decoded for network transmission.

In terms of the network, there have been key developments, e.g., IP Multicasting Protocol (which allows audio and videoconferencing between hundreds of participants) and the Real Time Protocol (which improves the functionality of multimedia conferences on the Internet). Multicasting allows a single multimedia stream to be sent to more than one destination without the need for a dedicated channel to each one.

However, it is a widely held belief that the Internet system does not have the reliability and consistent, guaranteed quality required for business applications of multimedia. As a result, business users are more likely to pursue the ISDN solution with conventional video CODECs.

The link between ISDN and multimedia prompted the formation of the Multimedia Communications Community of Interest (MCCI), which is a consortium of European, North American and Asia-Pacific carriers and vendors including IBM and Northern Telecom Ltd.

The other challenge to ISDN and circuit switching comes from Asynchronous Transfer Mode (ATM) which many regard to be the perfect network technology for multimedia. Once there is a requirement for real time video and bandwidth-on-demand, there is a requirement for ATM because it allows the flexible satisfaction of peaks in bandwidth demand. However, there are many more technical challenges facing the developers of ATM in terms of, for example, interoperability between wide area network (WAN) switches, as well as the reduction in cost per bit of an ATM connection, which at the moment is prohibitively expensive.

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